首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   402篇
  免费   18篇
  国内免费   18篇
耳鼻咽喉   1篇
儿科学   29篇
妇产科学   5篇
基础医学   31篇
口腔科学   4篇
临床医学   41篇
内科学   111篇
皮肤病学   11篇
神经病学   8篇
特种医学   59篇
外科学   58篇
综合类   21篇
预防医学   12篇
眼科学   4篇
药学   28篇
肿瘤学   15篇
  2022年   1篇
  2021年   2篇
  2020年   2篇
  2019年   2篇
  2018年   4篇
  2017年   2篇
  2016年   1篇
  2015年   5篇
  2014年   6篇
  2013年   11篇
  2012年   3篇
  2011年   4篇
  2010年   10篇
  2009年   19篇
  2008年   13篇
  2007年   28篇
  2006年   17篇
  2005年   16篇
  2004年   10篇
  2003年   10篇
  2002年   6篇
  2001年   20篇
  2000年   13篇
  1999年   9篇
  1998年   14篇
  1997年   13篇
  1996年   19篇
  1995年   8篇
  1994年   19篇
  1993年   13篇
  1992年   8篇
  1991年   4篇
  1990年   3篇
  1989年   19篇
  1988年   9篇
  1987年   12篇
  1986年   18篇
  1985年   11篇
  1984年   10篇
  1983年   9篇
  1982年   7篇
  1981年   9篇
  1980年   7篇
  1979年   1篇
  1978年   1篇
  1977年   6篇
  1975年   3篇
  1973年   1篇
排序方式: 共有438条查询结果,搜索用时 342 毫秒
91.

Background  

A dominant view in numerical cognition is that numerical comparisons operate on a notation independent representation (Dehaene, 1992). Although previous human neurophysiological studies using scalp-recorded event-related potentials (ERPs) on the numerical distance effect have been interpreted as supporting this idea, differences in the electrophysiological correlates of the numerical distance effect in symbolic notations (e.g. Arabic numerals) and non-symbolic notations (e.g. a set of visually presented dots of a certain number) are not entirely consistent with this view.  相似文献   
92.
93.
Journal of NeuroVirology - COVID-19 pandemic spreads worldwide, with more than 100 million positive cases and more than 2 million deaths. From the beginning of the COVID-19 pandemic, several...  相似文献   
94.
Factor IX Hilo is a variant factor IX molecule that has no detectable coagulant activity. The defect in factor IX Hilo arises from a point mutation in the gene such that in the protein Arg180 is converted to a Gln. Activation of factor IX Hilo by factor Xla was monitored using the fluorescent active site probe p-aminobenzamidine. Normal factor IX showed complete activation in one hour as determined by measuring the increase in fluorescence when p-aminobenzamidine bound to activated factor IX. Factor IX Hilo showed no increase in fluorescence even after 24 hours, indicating that the active site was not exposed. Polyacrylamide gel electrophoresis showed that factor IX Hilo was cleaved to a light chain plus a larger peptide with a molecular weight equivalent to a heavy chain covalently linked to an activation peptide. Amino terminal amino acid sequencing of factor IX Hilo cleaved by factor Xla showed cleavage only at Arg145-Ala146, indicating that the Gln180-Val181 bond was not cleaved and that the active site was thus not exposed. The presence of factor IX Hilo in patient plasma was responsible for the patient having a very long ox brain prothrombin time characteristic of severe hemophilia Bm. Patient plasma had an ox brain prothrombin time of 100 seconds using a Thrombotest kit, significantly prolonged over the normal control value of 45 seconds. When factor IX Hilo was depleted from patient plasma using an immunoaffinity column, the ox brain prothrombin time decreased to 41 seconds. When factor IX Hilo was added back to depleted patient plasma, to normal plasma depleted of factor IX by the same affinity column, or to plasma from a CRM- hemophilia B patient, the ox brain prothrombin time was significantly prolonged. We conclude that the Arg180 to Gln mutation in factor IX Hilo results in a molecule that cannot be activated by factor Xla. Further, our data suggest that the mutation results in a molecule that interacts with components of the extrinsic pathway to give a prolonged ox brain prothrombin time.  相似文献   
95.
豚鼠脂肪干细胞的分离培养与鉴定   总被引:1,自引:4,他引:1  
目的:从成年雄性豚鼠脂肪中分离培养脂肪干细胞,为脂肪干细胞移植治疗感音神经性耳聋的实验研究创造条件。方法:实验于2005-12/2006-03在河南省高等学校临床医学重点学科开放实验室完成。成年雄性豚鼠,体质量500~750g。分离培养豚鼠脂肪组织,培养三四天后首次换液。倒置显微镜下观察有大量细胞贴壁和漂浮的血细胞,用磷酸缓冲液反复冲洗去除漂浮的细胞,加入DMEM基础培养基 10%胎牛血清培养液。传代前用少量磷酸缓冲液洗涤1次,加入0.25%胰蛋白酶和0.02%乙二胺四乙酸2mL,见大部分细胞胞质回缩、形态变圆,加入2mL含血清的DMEM培养液终止消化,收集细胞悬液、计数,以2×104/cm2细胞密度接种于新的培养皿内。二三天达到融合状态,继续传代培养。四甲基偶氮唑蓝测定第1、3、10代脂肪干细胞生长曲线,流式细胞仪检测脂肪干细胞表面标志。结果:①原代培养显示培养的脂肪间充质干细胞2d左右开始贴壁,7d左右可达90%融合,基本上为梭形成纤维样细胞形态。②生长曲线显示,豚鼠脂肪干细胞在1~3代增值能力较强,以第1代细胞最强,10代以后增殖能力减弱,细胞生长进入平台期。经消化传代后的第1、3、10代细胞均经历24~48h的潜伏期,此后为3~5d对数生长期,逐渐进入生长平台期。14代以前具有活跃的增殖能力。③脂肪干细胞标志CD105,CD44呈阳性表达,而造血干细胞标志CD34阴性表达。结论:成功地建立了一种分离培养豚鼠脂肪间充质干细胞的方法,其生长稳定、增殖较快,可作为干细胞移植治疗感音神经性耳聋实验研究的供体细胞。  相似文献   
96.
In patients with chronic heart failure cardiac beta-1 adrenoceptors are reduced, whereas beta-2 adrenoceptor changes vary depending on the etiology of the disease. Beta Adrenoceptor agonists can be used for short-term inotropic support in chronic heart failure; their clinical efficacy might depend on which beta adrenoceptor subtype(s) mediates their positive inotropic effect. Thus, the beta adrenoceptor subtype(s) involved in the positive inotropic effects of clinically used beta adrenoceptor agonists was characterized on isolated electrically driven human right atria by the use of the selective beta-1 adrenoceptor antagonist CGP 20712 A (300 nmol/l) and/or the selective beta-2 adrenoceptor antagonist ICI 118,551 (30 nmol/l). Epinine evoked positive inotropic effects through stimulation of beta-1 and beta-2 adrenoceptors to about the same degree, whereas dobutamine acted mainly at beta-1 adrenoceptors but had a significant beta-2 adrenoceptor component. Both agonists were full agonists causing the same maximum increase in contractile force (Emax) as did isoprenaline or Ca++ (Emax = 1.0). In contrast, denopamine was a partial selective beta-1 adrenoceptor agonist (Emax = 0.75-0.85). Dopamine was in the presence of uptake1-blockade (by 5 mumol/l phenoxybenzamine) a partial agonist (Emax = 0.60-0.70) acting selectively at beta-1 adrenoceptors; in the absence of uptake1-blockade, however, dopamine was a full agonist, indicating that part of its positive inotropic effect is indirect via the release of endogenous noradrenaline. Xamoterol did not exert positive inotropic effects, but concentration-dependently slightly decreased basal force of contraction.  相似文献   
97.
目的:分析非亲缘异基因外周血干细胞移植治疗幼儿急性非淋巴性白血病的可行性。方法:患儿,男,3岁,于2005-07-18为行造血干细胞移植入本院血液科骨髓移植病房,入院诊断为急性非淋巴细胞性白血病-M5b。经抗肿瘤药物治疗病情获得完全缓解。患儿首先接受清髓性预处理,然后接受同性别非亲缘异基因外周血造血干细胞移植。①移植预处理包括马利兰、阿糖胞苷和环磷酰胺。移植前依次用药为马利兰3.2mg/(kg·d)×4d,口服,于移植前6,7,8,9d给药;阿糖胞苷3.2g/(m2·d)×2d,于移植前4,5d给药;环磷酰胺54mg/(kg·d),于移植前2,3d给药。②急性移植物抗宿主病的预防用药包括环孢菌素A和氨甲蝶呤、抗胸腺细胞球蛋白及吗替麦考酚酯。供者接受粒细胞集落刺激因子动员4d后采集外周血造血干细胞,供、受者间HLA全相合,患者血型A,供者血型B,主次要均不合。结果:①患儿移植后早期获得造血重建,中性粒细胞>0.5×109L-1和血小板>50×109L-1的天数分别是12d和11d。②移植后1个月经DNA短串联重复序列多态性分析证明为供者型完全植入,移植后3个月查骨髓象正常。③移植后3,6个月定期行淋巴细胞亚群检查表明除CD19 ,CD4 细胞未恢复外,自然杀伤细胞在移植后3个月恢复正常,T淋巴细胞CD3 与CD8 、体液免疫球蛋白在移植后6个月中均获得重建。④整个移植过程顺利,未出现明显感染和重度急性移植物抗宿主病。移植后96d时出现Ⅰ度皮肤移植物抗宿主病,经加用激素治疗,皮疹消失。移植术后已随访观察12个月,患儿正常生活。结论:如果患儿有HLA完全相合的供者,非亲缘异基因外周血干细胞移植治疗儿童高危白血病是一种有效和安全的方法,对国内独生子女家庭拓宽供者来源有重要的实用价值。  相似文献   
98.
The presence of heart rate variability (HRV) in patients with cardiac denervation after heart transplantation raised our interest in HRV of isolated, denervated hearts. Hearts from seven adult white ELCO rabbits were transferred to a perfusion apparatus. All hearts were perfused in the working mode and in the Langendorff mode for 20 minutes each. HRV was analyzed in the frequency domain. A computer simulated test ECG at a constant rate of 2 Hz was used for error estimation of the system. In the isolated, denervated heart, HRV was of random, broadband fluctuations, different from the well-characterized oscillations at specific frequencies in intact animals. Mean NN was 423 ± 51 ms in the Langendorff mode, 406 ± 33 ms in the working heart mode, and 500 ms in the test ECG. Total power was 663 ± 207 ms2, 817 ± 318 ms2, and 3.7 ms2, respectively. There was no significant difference in any measure of HRV between Langendorff and working heart modes. The data provide evidence for the presence of HRV in isolated, denervated rabbit hearts. Left atrial and ventricular filling, i.e., the working heart mode, did not alter HRV, indicating that left atrial or ventricular stretch did not influence the sinus nodal discharge rate.  相似文献   
99.
Lijnen  HR; Van Hoef  B; De Cock  F; Collen  D 《Blood》1989,73(7):1864-1872
The relative contribution of several mechanisms to plasminogen activation and fibrin dissolution by urokinase-type plasminogen activator (u-PA) in vitro was quantitated. The activation of plasminogen by recombinant single chain u-PA (rscu-PA), by its two chain derivative (rtcu-PA) and by a plasmin-resistant mutant, rscu-PA- Glu158, obeys Michaelis-Menten kinetics with catalytic efficiencies of 0.00064, 0.046, and 0.00005 L/mumol.s for native plasminogen (Glu- plasminogen) and of 0.0061, 1.21, and 0.0004 L/mumol.s for partially degraded plasminogen (Lys-plasminogen). In a purified system consisting of a fibrin clot submerged in a plasminogen solution, the equi- effective doses (50% lysis in one hour) for rscu-PA, rtcu-PA, and rscu- PA-Glu158 were 16, 6.5, and 32,000 ng/mL for Glu-plasminogen and two- to fourfold lower for Lys-plasminogen. In a plasma milieu, 50% lysis in two hours was obtained for a plasma clot with 2.1 micrograms/mL rscu- PA, 0.5 micrograms/mL rtcu-PA, and greater than 200 micrograms/mL rscu- PA-Glu158 and for a purified fibrin clot with 1.3 micrograms/mL rscu-PA and 0.27 microgram/mL rtcu-PA. After predigestion of a purified fibrin clot with plasmin, the apparent potency of rscu-PA and rtcu-PA increased by 40% and 20%, respectively. In conclusion, rscu-PA has an intrinsic plasminogen activating potential that is only about 1% of that of rtcu-PA and that is 13 times higher than that of rscu-PA- Glu158. Conformational transition of Glu-plasminogen to Lys-plasminogen enhances its sensitivity to activation by all u-PA moieties ten- to 20- fold. Predigestion of fibrin clots with associated increased binding of plasminogen results in a minor apparent increase of the fibrinolytic potency of rscu-PA and rtcu-PA. The relative fibrinolytic potency of rtcu-PA is two to three orders of magnitude higher than that of rscu-PA- Glu158 but only two- to five-fold higher than that of rscu-PA, both in purified systems and in a plasma milieu. These results indicate that conversion of rscu-PA to rtcu-PA constitutes the primary mechanism of fibrin dissolution.  相似文献   
100.
Melhem  MF; Meisler  AI; Saito  R; Finley  GG; Hockman  HR; Koski  RA 《Blood》1993,82(7):2038-2044
Inflammatory malignant fibrous histiocytomas (IMFH) are rare tumors and are frequently associated with leukocytosis. In rare cases, leukemoid reactions were attributed to tumor production of unidentified hematopoietic factors. In this study, we used immunohistochemical techniques to show cytokine immunoreactivity in the malignant cells of two cases of IMFH presenting with leukemoid reactions and compared them with two malignant fibrous histocytomas, noninflammatory type. All four tumors stained positively for stem cell factor (SCF), granulocyte colony-stimulating factor (G-CSF), interleukin-2 (IL-2), IL-4, IL-5, interferon-alpha (IFN-alpha), and insulin-like growth factor-I. Other cytokines detected only in the two IMFH included IL-6, IL-7, IL-8, IFN- gamma, and keratinocyte growth factor. Granulocyte-macrophage-CSF, IL- 3, and transforming growth factor-beta staining was present in one of the two IMFH tumors and was not present in the noninflammatory tumors. The immunohistochemical staining was localized to the malignant cells, suggesting deregulated cytokine expression consistent with their monocytic/histocytic origin. Expression of certain cytokines in the IMFH may account for the local inflammatory infiltrate, tumor fibrosis, and the aggressive nature of the malignant cells. We also detected elevated serum levels of SCF, G-CSF, IL-6, and tumor necrosis factor in one or both of the IMFH patients. These latter observations may explain the bone marrow hypercellularity and other paraneoplastic symptoms, including fever, malaise, and weight loss, observed in both patients. Different cytokines present in the two IMFH tumors appear to be responsible for the eosinophilic leukemoid reaction observed in one case and for the granulocytic leukemoid reaction observed in the other patient. They may also be responsible for expansion of the tumor-cell population, fibroblast proliferation, and enhanced secretion of extracellular collagen.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号